Concentric evaporation-condensation, rotary, thin film, heat transfer apparatus

ABSTRACT

The invention relates to an apparatus for transfer of heat between solids, liquids and vapors and for transfer of mass between and within liquids and vapors, the apparatus comprising a rotatable, substantially cylindrical film carrier onto which a thin film of a material to be vaporized is deposited by stationary depositing means, a vaporizing zone surrounding the film carrier, and a condensation zone within the film carrier into which a vaporized component of the material deposited on the film carrier is directing for condensing. The film carrier constitutes a common heat transfer boundary between the vaporizing and condensation zones and latent heat emitted from material during condensation passes through the film carrier to effect the vaporization of the material on the outside of the film carrier. The invention has particular application as a desalination apparatus.

United States Patent [72] Inventor Arthur K. Johnston New Lambton, New South Wales, Australia [21] Appl. No. 814,352 [22] Filed Apr. 8, 1969 [45] Patented May 11, 1971 [73] Assignee The University of Newcastle Newcastle, New South Wales, Australia [32] Priority Apr. 11, 1968 [33] Australia [31] 36388/68 [54] CONCENTRIC EVAPORATION-CONDENSATION,

ROTARY, THIN FILM, HEAT TRANSFER APPARATUS 9 Claims, 6 Drawing Figs.

[52] U.S. Cl 165/66, 202/187, 202/205, 202/236, 202/238, 203/11, 203/89, 165/86, 159/12, 159/49 [51 Int. Cl F281 5/00 [50] Field of Search 202/ 187, 235-238, 205; 203/89, 90, 91,10,11;159/12, 49; 165/66, 86

[56] References Cited UNITED STATES PATENTS 830,521 9/ 1906 Passburg 159/12 1,353,980 9/1920 Yahn 159/12 1,501,514 7/1924 Boberg... 159/12 1,501,515 7/1924 Testrup 202/236UX 2,581,081 1/1952 De Vout 159/12X 3,326,266 6/ 1967 Braithwaite et a1 159/ 12X Primary Examiner-Norman Yudkoff Assistant ExaminerDavid Edwards Att0rneySinger, Stern and Carlberg ABSTRACT: The invention relates to an apparatus for transfer of heat between solids, liquids and vapors and for transfer of mass between and within liquids and vapors, the apparatus comprising a rotatable, substantially cylindrical film carrier onto which a thin film of a material to be vaporized is deposited by stationary depositing means, a vaporizing zone surrounding the film carrier, and a condensation zone within the film carrier into which a vaporized component of the material deposited on the film carrier is directing for condensing. The film carrier constitutes a common heat transfer boundary between the vaporizing and condensation zones and latent heat emitted from material during condensation passes through the film carrier to effect the vaporization of the material on the outside of the film carrier. The invention has particular application as a desalination apparatus.

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qcmmmmlzmu E n m .A n- M I CONCEN'I RIC EVAPORATION'CONDENSATION, ROTARY. THIN FILM, HEAT TRANSFER APPARATUS This invention relates to an apparatus for, and to a method of, transferring heat between solids, liquids and vapors and transferring mass between and/r within liquids and vapors; the invention being concerned especially with evaporation and condensation of fluids.

More particularly, the invention relates to an apparatus in which evaporation is effected from a thin film of liquid on a solid carrier and/or in which condensation occurs in a like thin film ofa fluid on a solid carrier.

Apparatus which is known to have been heretofore employed and which embodies this mode of operation for effecting heat transfer falls into two groups, one in which a liquid to be evaporated is deposited as a stream onto the apex end of a horizontally disposed rotating conical film carrier, and the other in which a thin film of liquid to be evaporated is wiped onto the inside or outside surface of a stationary vertically disposed cylindrical film carrier.

In the apparatus employing the conical-shaped film carrier, a film thickness differential occurs between the small (apex) and and the large diameter (or base) end of the cone due to the centrifugal force gradient between the small and large ends of the cone. This results in uneven migration and thickness of the liquid between the ends of the film carrier and hence a buildup of a concentrated solution of the liquid in the area of the small end of the cone. Such condition may be conducive to scale formation and result in uneven heat transfer through the carrier.

Similarly, in the apparatus employing a vertically disposed carrier, the fluid wiped thereon is subject to the effect of gravity and it is thus caused to migrate downwardly along the wall of the carrier to establish a temporarily nonuniform film thickness and a variation in concentration longitudinally on the carrier.

An object of the present invention is to provide for efficient and economical transfer of latent heat involved in evaporation and/or in condensation of a fluid, and to provide an apparatus which obviates the drawbacks inherent in known prior art devices.

Thus, there is provided in accordance with the broadest aspect of the present invention, an apparatus for transfer of heat between solids, liquids and vapors or gases and for transfer of mass between and/or within liquids and vapors or gases, said apparatus comprising at least one vaporizing zone, at least one condensation zone, a rotatable, substantially cylindrical film carrier disposed between the or each respective said vaporizing and condensation zones and constituting a common heat transfer boundary for the or each respective said vaporizing and condensation zones, stationary means for depositing onto said film carrier(s) a filmof a material to be transformed from a liquid state to a vapor state within said vaporizing zone(s), means for introducing into said condensation zone(s) a vapor for condensing onto said film carrier(s) within the condensation zone(s), means for removing or per mitting removal of condensate from the film carrier(s) within the condensation zone(s), and means for removing or permitting removal of said material in its vapor state from the vaporizing zone.

In accordance with the present invention, heat liberated from condensing fluid in said condensing zone(s) provides at least a component of necessary vaporizing heat and said film carrier(s) constitute(s) a .solid" heat transfer medium between said condensing and vaporizing zone(s).

The present invention also provides amethod for transfer of heat between solids, liquids and vapors or gases and for transfer of mass between and/or within liquids and vapors; said method being performed by the employment of an apparatus substantially as above defined.

One application of the present invention is in the distillation of liquids and wherein a liquid is caused or is permitted to evaporate on one side of a solid carrier while another liquid condenses on the other side of the same carrier. However it will be appreciated that the invention need not be limited to concurrent evaporation and condensation of a single fluid, although the invention is hereinafter described in this context.

The present invention has a particular application in the production of fresh water from salt water and a preferred embodiment of an apparatus for this purpose is hereinafter described by way of example with reference to the accompanying schematic drawings. However the invention may equally well be applied to the evaporation and condensation of other liquids, or to other heat and mass transfer processes involving liquids, vapors and gases.

In the drawings:

FIG. I illustrates an end view, in section, of one form of the apparatus in accordance with the present invention, said end view being completely diagrammatic and constructional features of the apparatus being omitted therefrom;

FIG. 2 shows, in greater detail, a diagrammatic side elevation view of the apparatus taken along plane 2-2 of FIG. 1;

FIGS. 3 and 4 show an end view and a sectional side view respectively of a preferred constructional form of a film carrier for journal mounting in the apparatus;

FIG. 5 shows an end view (similar to FIG. I) of a second form of the apparatus; and

FIG. 6 shows an end view (similar to FIG. 1) of a third form of the apparatus.

The apparatus as shown in the drawings comprises, generally, an outer preferably cylindrical container 10 which is adapted to retain a pool of salt water 11 in the lowermost portion thereof, and a rotatable film carrier 12 mounted axially within the container.

The film carrier preferably comprises a thin walled metal tube, as hereinafter described, or a hollow cylinder, which has its ends closed but for ports 13 (FIG. 2) which are arranged for the removal of a liquid medium from the interior of the film carrier 12. Also, the film carrier is journaled for rotation through shafts l4 and 15 with its longitudinal axis in a horizontal plane, such that it may be rotated with a lower zone 16 of its outer surface in constant contact with the pool of salt water I l.

The interior of the film carrier constitutes a condensation zone 17 and an annular space defined by the film carrier 12 and the internal wall of the cylindrical container 10 comprises an evaporation zone 18, both of which zones are hereinafter referred to.

Means such as, for example, an electric motor are provided for rotatably driving the film carrier 12 through a belt driven pulley 19, the peripheral velocity of the driven film carrier being in the order of, for example, 20 to 50 feet.sec. for a film carrier diameter of, for example, 4 inches.

Thus, when the film carrier 12 is rotated, the external surface of the carrier emerging from the pool of salt water 11 carries with it a thin film of liquid, a portion at least of which evaporates during the time in which it is exposed in said evaporation zone 18, above the pool surface. Where the entire liquid film is not evaporated, the unevaporated portion thereof (which may, for example, be in the order of 30 percent) is returned to a discharge zone 20 as brine; that is, as a more concentrated solution than the original salt water.

Salt water to be purified is fed into the pool 11 through an inlet conduit 21 and any unevaporated solution is washed from the film carrier 12 in the discharge zone 20 and is withdrawn from the discharge zone through an outlet conduit 22. Washing water is provided to the discharge zone through inlet conduit 22a.

A resilient, or resiliently mounted, doctor blade 23 is preferably mounted below the film carrier 12 such that it extends longitudinally within the container 10 to wipe against the outer surface of the film carrier, during its rotation, at a point near where it leaves the pool surface. Such doctor blade ensures that the liquid film entrained on the film carrier will be kept very thin (for example, in the order of 0.0001 to 0.0005 inches thick), whereby the water component of the film will be caused to rapidly evaporate.

A second resilient or resiliently mounted wiper blade 24 is located in the discharge zone 20 below the film carrier, but before the first mentioned blade 23 in the direction of rotation of the carrier, to assist in removing any unevaporated solution or salt from the carrier into the discharge zone 20 prior to a subsequent-revolution of the carrier.

Again, the doctor blade(s) 23 and/or 24 may be replaced by a compressed pad of a porous material, such as estafoam or a nylon or teflon wool, and such pad may extend for the arcuate length of the pool 11. Or there may be a multiplicity of pads (some of which may be mildly abrasive), for separate operations of washing and wiping the carrier, and, thereafter, feeding the liquid film onto the carrier. In FIG. there is shown a pad 25 for applying the thin film to the film carrier 12, while in H0. 6 there is shown a pad 26 for wiping unevaporated solution from the film carrier.

Also shown in FIG. 6 is an alternative method of applying a thin film of liquid to be evaporated to the film carrier 12. Thus, there is shown a jet 26 which is fed through a conduit 27 with a pressurized supply of the salt water to be evaporated and a deflecting shield 28 surrounding the jet 26 which is adapted to receive and carry-away from the evaporation zone 18 any liquid which is delivered by the jet but which is not held captive on the film carrier 12 under the influence of surface tension. It will be appreciated however that, with this arrangement, due consideration would have to be given to the centrifugal force field established by the rotating film carrier and the surface tension characteristics which prevail between the salt water and the film carrier in computing the pressure at which the salt water is delivered, in order to obviate a condition where no salt water film will actually remain on the film carrier.

That component of the delivered salt water which does not form a film on the film carrier may be discharged through a conduit 29 into the discharge conduit 22 to combine with the unevaporated salt solution wiped from the film carrier by the pad 26.

Condensation of the vaporized fluid is effected in the condensation zone 17, to which the vapor is transferred (from the vaporizing zone), and latent heat given off during the change of state (from vapor to liquid) is transferred through the cylindrical wall of the film carrier 12 to the evaporating zone 18 outside the film carrier. The vapor may be delivered to the condensation zone 17, from the vaporizing zone 18, (at a desired temperature and pressure) through a compressor (not shown) or other means which draws from the evaporation zone, and by way of outlets 31, conduits 32 and a diffuser element 33.

The vapor so condensed forms pure water (or substantially pure water) on the inside surface of the film carrier 12 and such water is removed from said inner wall by it being caused to migrate, under the influence of the centrifugal field, toward peripherally apertured channels 34 formed at each end of the film carrier. In this way the liquid film on the inner wall of the carrier 12 may be maintained at substantially the same thickness as that on the outer peripheral wall of the carrier and the condensate which migrates into the channels 34 will be removed therefrom, also under the influence of the centrifugal field, by it passing through the apertures 13 into associated stationary channels 36. The condensate is thereafter removed from the channels 36 through discharge pipes 37.

From an operational aspect, the thinner the inner and outer films are, the thinner the film carrier wall thickness is and the better conductor the film carrier material is, the less will be the thermal resistance across the composite boundary and the more efficient will be the process. The evaporating film on the outside of the film carrier 12 may readily and economically be kept thin by wiping as aforedescribed. The condensing film might also be kept thin by a wiper blade 40 (see FIG. 6) located within the condensation zone 17.

Preferably, however, the interior wall of the cylindrical film carrier 12 is formed with longitudinal flutes 38 and channels 39 (as shown in FIGS. 3 and 4) whereby vapor entering the condensation zone 17 will condense on the flutes 38 and be forced by centrifugal action into the channels 39, from which the water will flow into the collector channels 34 located at one or both ends of the film carrier 12. With this construction the peripheral velocity and the diameter of the film carrier 12 may be arranged to ensure that the liquid film on the flutes is kept thin and that the depth of liquid in the channels is kept small.

The crests 40 of the flutes are preferably sloped or made convex such that the fluid will tend to run down"'the slope and into the channel under the influence of the centrifugal field, and the proportions of the dimensions A, B, C, and E (as shown in FIG, 3) are chosen to achieve an optimum condition taking into account the following conflicting factors:

1. If A and C are made too large they add thermal resistance to heat transfer across the film carrier, but they must be made large enough to achieve a desired mechanical strength and to provide a sufficient depth C for the channel.

2. If E is made too narrow, the channel will not handle the required flow of condensate and the capacity of the apparatus will be impaired, but if E is made too large it takes away from D which is a useful heat transfer area.

Thus, the proportions of the referenced dimensions would have to be computed having regard to specific conditions and requirements.

Variations and modifications may be made in the apparatus as hereinbefore specifically described and illustrated without departing from the scope of the appendent claims. For example, although the apparatus has been aforedescribed as having a horizontal film carrier 12 it will be appreciated that where a porous material is employed for wiping and feeding the salt water onto the film carrier, horizontal placement may not be necessary and any inclination to a gravity field may be adopted, provided the salt water is unifonnly distributed onto the film carrier 12 along its longitudinal extent. The apparatus would thus be usable under conditions of weightlessness or varying gravitational fields.

Again, there may be a plurality of carriers similar to that (or those) above described arranged in cascade. In such instance, the interior of the film carrier of the first unit of apparatus of the cascade may be heated by steam derived, for example, from a conventional steam generator and the vapor produced in the vapor zone of the first unit may be fed to the condensation zone of the second unit where it condenses into fresh water and, at the same time, delivers-up heat to produce vapor in the evaporation zone of the second unit. The third unit may then be fed with vapor from the second unit, and so on.

In another possible embodiment there may be a number of concentric annular vaporization and condensation zones, each being defined by concentric rotatable film carriers, located withina single container or housing.

According to yet another embodiment of the invention, the evaporation and condensation zones may be respectively located at the inside andthe outside of the film carrier. In such case, the salt water may be fed into a pool on the inside of the film carrier, the pool being retained in position by a wiper blade, and a spend water outlet be provided for removing brine solutions from the pool. Then, the condensed fresh water on the outside of the film carrier may be removed by either a scraper or by centrifugal action.

lclaim:

1. An apparatus for transfer of heat comprising a vaporizing zone, a condensation zone, a rotatable substantially cylindrical film carrier which is disposed within said vaporizing zone and about said condensation zone and which constitutes a common heat transfer boundary between said zones, stationary means adapted to deposit onto said film carrier a film of a material to be transformed from a liquid state to a vapor state within said vaporizing zone, compressor means for transferring a vaporized component of said material from said vaporizing zone into said condensation zone wherein it condenses to a form a film of condensate on said film carrier, means for wiping residual material from the film carrier within the vaporizing zone, and means for removing said condensate from the film carrier; the inside surface of the film carrier being defined by a plurality of circumferentially spaced longitudinally extending flutes wherein each flute is formed with a sloped crest, said flutes defining channels in which said film of condensate forms under the influence of a centrifugal field established by rotation of the film carrier wherein said channels are defined by sidewalls which taper inwardly toward the bottom of the channels.

2. An apparatus as claimed in claim I, wherein said film carrier is provided at, at least one end thereof with annularly spaced condensate outlet ports, said outlet ports constituting the means for permitting removal of condensate from the film carrier.

3. An apparatus as claimed in claim I. wherein said film carrier is horizontally disposed, said material in its liquid state is retained in a pool below and in contact with a peripheral portion of said film carrier, and said stationary film depositing means comprises a doctor blade which contacts said peripheral portion adjacent where the film carrier exits from the pool to wipe said material onto the film carrier to form said film.

4. An apparatus as claimed in claim 1, wherein said film carrier is horizontally disposed, said material in its liquid state is retained in a pool below and in contact with a peripheral portion of said film carrier, and said stationary film depositing means comprises an absorbent pad located within said pool and in contact with at least a portion of said peripheral portion of the film carrier to wipe a uniform said film of said material onto the film carrier.

5. An apparatus as claimed in claim 1, including a discharge zone located in contact with the film carrier for removing unevaporated solution from the film carrier subsequent to its passage through the vaporizing zone.

6. An apparatus as claimed in claim 5, said discharge zone comprising a washing zone and a wiper blade following the washing zone in the direction of rotation of the film carrier.

v7. An apparatus as claimed in claim 5, said discharge zone comprising at least one absorbent pad which is kept wetted with a washing solution or liquid.

8. An apparatus as claimed in claim 5, said discharge zone comprising pads which perform successive operations of washing and polishing the film carrier.

9. An apparatus as claimed in claim I, said means adapted for depositing the film of material onto the film carrier comprising at least one jet which directs said material against the surface of the film carrier under pressure, whereby at least a component of the directed material forms a surface film on the film carrier under the influence of a surface tension affect existing between the material and the film carrier surface. 

2. An apparatus as claimed in claim 1, wherein said film carrier is provided at, at least one end thereof with annularly spaced condensate outlet ports, said outlet ports constituting the means for permitting removal of condensate from the film carrier.
 3. An apparatus as claimed in claim 1, wherein said film carrier is horizontally disposed, said material in its liquid state is retained in a pool below and in contact with a peripheral portion of said film carrier, and said stationary film depositing means comprises a doctor blade which contacts said peripheral portion adjacent where the film carrier exits from the pool to wipe said material onto the film carrier to form said film.
 4. An apparatus as claimed in claim 1, wherein said film carrier is horizontally disposed, said material in its liquid state is retained in a pool below and in contact with a peripheral portion of said film carrier, and said stationary film depositing means comprises an absorbent pad located within said pool and in contact with at least a portion of said peripheral portion of the film carrier to wipe a uniform said film of said mAterial onto the film carrier.
 5. An apparatus as claimed in claim 1, including a discharge zone located in contact with the film carrier for removing unevaporated solution from the film carrier subsequent to its passage through the vaporizing zone.
 6. An apparatus as claimed in claim 5, said discharge zone comprising a washing zone and a wiper blade following the washing zone in the direction of rotation of the film carrier.
 7. An apparatus as claimed in claim 5, said discharge zone comprising at least one absorbent pad which is kept wetted with a washing solution or liquid.
 8. An apparatus as claimed in claim 5, said discharge zone comprising pads which perform successive operations of washing and polishing the film carrier.
 9. An apparatus as claimed in claim 1, said means adapted for depositing the film of material onto the film carrier comprising at least one jet which directs said material against the surface of the film carrier under pressure, whereby at least a component of the directed material forms a surface film on the film carrier under the influence of a surface tension affect existing between the material and the film carrier surface. 